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John Hawthorn - RubyConf mini 2022 Making is_a? Fast

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• Ruby Core Team • Rails Core Team • Sta ff Engineer @ GitHub John Hawthorn @jhawthorn @[email protected] he/him

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is_a? "Is this object of this class/module"

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"foo".is_a?(String) => true "foo".is_a?(Integer) => false 123.is_a?(Integer) => true 123.is_a?(Numeric) => true

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is_a?(Pigeon) Making is_a? Fast #

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String === x x.is_a?(String)

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• kind_of? • Module#=== • case statement • rescue statement • protected methods What is "is_a?" is_a?("is_a?")

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2% of total Ruby runtime* is_a? * In Rails apps I measured, your mileage may vary

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Profiling Ruby stackprof or rbspy

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$ stackprof benchmarks/railsbench/out.bench ================================== Mode: wall(1000) Samples: 32453 (0.00% miss rate) GC: 3699 (11.40%) ================================== TOTAL (pct) SAMPLES (pct) FRAME 1646 (5.1%) 1646 (5.1%) String#gsub! 2295 (7.1%) 698 (2.2%) Class#new 1375 (4.2%) 654 (2.0%) Jbuilder#_set_value 1139 (3.5%) 637 (2.0%) ActiveModel::Type::Hel 565 (1.7%) 565 (1.7%) Module#=== 554 (1.7%) 554 (1.7%) JSON::Ext::Generator::

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$ stackprof redacted_2022-11-02-14-23-11.stackprof.json ================================== Mode: wall(200) Samples: 64246 (4.57% miss rate) GC: 0 (0.00%) ================================== TOTAL (pct) SAMPLES (pct) FRAME 4725 (7.4%) 4725 (7.4%) IO#read 14203 (22.1%) 3278 (5.1%) Class#new 2513 (3.9%) 2513 (3.9%) Kernel#is_a? 2380 (3.7%) 2307 (3.6%) Trilogy#query

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Profiling C perf https://www.brendangregg.com/perf.html https://perf.wiki.kernel.org/index.php/Main_Page

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rb_define_method(rb_mKernel, "kind_of?", rb_obj_is_kind_of, 1); rb_define_method(rb_mKernel, "is_a?", rb_obj_is_kind_of, 1); rb_obj_is_kind_of src/ruby/object.c VALUE rb_obj_is_kind_of(VALUE obj, VALUE c);

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bool rb_obj_is_kind_of(VALUE obj, VALUE search) { return class_search_ancestor(CLASS_OF(obj), search); }

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bool class_search_ancestor(VALUE cl, VALUE search) { while (cl) { if (cl == c) return true; cl = RCLASS_SUPER(cl); } return false; } bool rb_obj_is_kind_of(VALUE obj, VALUE search) { return class_search_ancestor(CLASS_OF(obj), search); }

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def class_search_ancestor(klass, search) while klass return true if klass == search klass = klass.superclass end false end def rb_obj_is_kind_of(obj, search) class_search_ancestor(obj.class, search) end

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Butter fl y Object BasicObject Pidgeon

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Butter fl y Object BasicObject Pidgeon

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Butter fl y Object BasicObject Pidgeon

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Butter fl y Object BasicObject

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Butter fl y Object BasicObject

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Butter fl y Object BasicObject ICLASS ICLASS

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Butter fl y Object BasicObject ICLASS ICLASS

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Butter fl y Object PP::ObjectMixin Kernel BasicObject ICLASS ICLASS

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rb_obj_is_kind_of(obj, klass) def class_search_superclass(klass, search) while klass return true if klass == search klass = klass.superclass end false end def rb_obj_is_kind_of(obj, search) class_search_superclass(obj.class, search) end

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rb_obj_is_kind_of(obj, klass) def class_search_superclass(klass, search) while klass return true if klass == search klass = klass.superclass end false end def rb_obj_is_kind_of(obj, search) class_search_superclass(obj.class, search) end ObjectSpace.internal_super_of ObjectSpace.internal_class_of

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rb_obj_is_kind_of(obj, klass) def class_search_superclass(klass, search) while klass return true if klass == search klass = ObjectSpace.internal_super_of(klass) end false end def rb_obj_is_kind_of(obj, search) class_search_superclass(ObjectSpace.internal_class_of(class), sea end

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Butter fl y Object PP::ObjectMixin Kernel BasicObject ICLASS ICLASS CPU 😢 • cache lines • branch prediction

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klass klass.ancestors.size Object 11 Hash 19 Array 21 String 19 ActiveRecord::Base 72 ApplicationRecord::Base 80 ApplicationController 129 Repository 271 Organization 305

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What to do? Avoid is_a? - use instance_of? Simplify class hierarchy Improve is_a? Avoid is_a? - respond_to?

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Library/Framework Application Where to fix? Language Easy to change Hard to change Narrow fi x Broad fi x

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Let's fix it in CRuby

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Hash table Attempt #1

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hash = { Pidgeon => true, Object => true, PP::ObjectMixin => true, Kernel => true, BasicObject => true } # to test hash.include?(klass)

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def build_class_table(klass) hash = {} while klass hash[klass] = true klass = klass.super end hash end # to test hash.include?(klass)

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st_table *build_class_table(VALUE klass) { st_table *hash = st_build_numtable(); while (klass) { st_insert(hash, klass, Qtrue); klass = RCLASS_SUPER(klass); } return hash; } // to test st_lookup(hash, klass, NULL)

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🫤 Complex 🫤 Needs cache invalidation 🫤 Slower in best case 🫤 Lots of memory used ✅ Consistent performance ✅ Faster in worst case

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Attempt #2

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bool class_search_ancestor(VALUE cl, VALUE search) { rb_obj_info_dump(search); while (cl) { if (cl == search) return true; cl = RCLASS_SUPER(cl); } return false; }

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849127 T_CLASS Hash 466102 T_CLASS Array 270880 T_CLASS String 168829 T_CLASS ActionDispatch::Cookies::AbstractCookieJar 155889 T_CLASS Symbol 124974 T_CLASS Numeric 91594 T_CLASS NilClass 83328 T_CLASS Jbuilder::Blank 76853 T_CLASS TrueClass 76213 T_CLASS FalseClass 69976 T_CLASS URI::Generic 62189 T_CLASS ActionController::Parameters 60719 T_CLASS (annon) 57980 T_CLASS (annon) 50100 T_CLASS Concurrent::Collection::MriMapBackend 49742 T_CLASS ActiveSupport::HashWithIndifferentAccess 45199 T_ICLASS src:ActionDispatch::Routing::UrlFor 39851 T_CLASS ActiveRecord::Relation 39836 T_CLASS Proc 39320 T_CLASS BigDecimal 31648 T_CLASS Range 29861 T_CLASS Pathname 29848 T_CLASS ActiveSupport::OrderedOptions

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Class only linked list Attempt #2

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Butter fl y Object PP::ObjectMixin Kernel BasicObject ICLASS ICLASS

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🫤 Still loops 🫤 Still O(N) 🫤 Still linked list ✅ Simple ✅ No cache invalidation

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Array Attempt #3

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Butter fl y Object PP::ObjectMixin Kernel BasicObject ICLASS ICLASS

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Butter fl y Object PP::ObjectMixin Kernel BasicObject

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Butter fl y PP::ObjectMixin Kernel BasicObject Object

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Butter fl y PP::ObjectMixin Kernel BasicObject Object

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Butter fl y BasicObject Object

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception Object BasicObject

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception Object BasicObject

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception Object BasicObject

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TypeError Exception Object BasicObject StandardError TypeError is_a? Exception Exception Object BasicObject ✅

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TypeError Exception Object BasicObject StandardError TypeError is_a? Hash Hash Object BasicObject 🚫

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TypeError Exception Object BasicObject StandardError TypeError is_a? Integer Numeric Object BasicObject Integer 🚫

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TypeError Exception Object BasicObject StandardError TypeError is_a? StandardErro Exception Object BasicObject StandardError ✅

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TypeError Exception Object BasicObject StandardError TypeError is_a? Object Object BasicObject ✅

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def class_search_superclass(klass, search) depth = search.superclasses.size - 1 klass.superclasses[depth] == search end

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def class_search_superclass(klass, search) depth = search.superclasses.size - 1 klass.superclasses[depth] == search end ✅ O(1) "constant time" ✅ No loops ✅ No cache invalidation

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Time-memory trade-off GitHub's largest application: 92k Classes 😳 Memory increase: +6.6 MB Before: ~88MB used by classes

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Exception Object BasicObject StandardError TypeError Exception Object BasicObject StandardError NameError Exception Object BasicObject StandardError RuntimeError TypeError NameError RuntimeError

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Exception Object BasicObject StandardError Exception Object BasicObject StandardError Exception Object BasicObject StandardError TypeError NameError RuntimeError

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Exception Object BasicObject StandardError TypeError NameError RuntimeError

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Time-memory trade-off GitHub's largest application: 92k Classes 😳 Memory increase: +6.6 MB Memory increase: +1.1 MB Before: ~88MB used by classes

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def class_search_superclass(klass, search) depth = search.superclasses.size klass.superclasses[depth] == search end

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def class_search_superclass(klass, search) return true if klass == search depth = search.superclasses.size klass.superclasses[depth] == search end

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def class_search_superclass(klass, search) return true if klass == search depth = search.superclasses_size return false if klass.superclass_size <= depth klass.superclasses[depth] == search end

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bool class_search_superclass(VALUE klass, VALUE search) if (klass == search) return true; int depth = search.superclasses_size; if (klass.superclass_size <= depth) return false; return klass.superclasses[depth] == search; end

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Always faster!

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thanks ❤

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Related PRs • https://github.com/ruby/ruby/pull/5568 (fast class checks) • https://github.com/ruby/ruby/pull/5604 (memory reduction)